1. Field of the Invention
This invention relates generally to touchpad technology. More specifically, the present invention is a new method of determining the position of a pointing object on a surface capacitance touch panel.
2. Description of Related Art
A well-known touchpad technology uses a surface capacitance touch panel 10 as shown in FIG. 1. Such a touch panel 10 is a solid sheet of a conductive material 16 disposed on an insulating substrate 18 such as glass, with sensors 12 disposed at the corners. The traditional method of measuring the position of a pointing object 14 or the “touch position” on the surface capacitance touch panel 10 is to apply an AC signal on all four corners of the touch panel's conductive layer 16. The conductive layer 16 can be made, for example, of Indium Tin Oxide (ITO).
To create the touch panel 10, the surface of the glass substrate 18 is flooded or covered with a substantially even layer of a resistive ITO material which forms a sheet resistance. A dielectric is then applied to cover the ITO conductive material.
After applying the AC signal to the conductive ITO material 16, the next step is to triangulate the touch position using the current flowing through each corner. It is common to apply either a sine wave or a square wave.
If an object such as a finger 14 comes in contact with the surface of the touch panel 10, a capacitor is formed between the ITO surface 16 and the finger tip 14. The capacitance value is very small, typically in the order of 50 pF. The amount of charge or current that has to be measured going into each corner 12 of the panel is therefore very small. Because the current is so small, the system is very susceptible to stray capacitance. Thus, the accuracy of touch panels 10 is often an issue.
Accordingly, what is needed is a new method of triangulating the position of the object on the touch panel surface that increases the accuracy of measurements and decreases susceptibility to stray capacitance.